In an automotive engine, it is necessary to measure an intake air flow rate in order to control a fuel injection amount. The intake air flow rate is measured, for instance, by a heat generation resistor type gas flow rate measurement device. It is preferred that the output signal of the heat generation resistor type gas flow rate measurement device vary insignificantly even when a temperature change occurs, namely, exhibit an insignificant temperature-dependent error. To reduce the temperature dependent error, it is necessary to correct a temperature dependent error in a gas flow rate detection signal in accordance with a gas temperature/substrate temperature detection signal.
A gas temperature dependent error is corrected, for instance, by a technology described in Japanese Unexamined Patent Application Publication No. Hei 11 (1999)-37815. This technology is exercised so that the temperature detection signal of a thermistor or other independent temperature sensor disposed in an intake air flow path is used to perform digital computations and correct the gas temperature dependent error. In general, the thermistor used as a temperature sensor has an advantage in that it is inexpensive. However, its resistance value is an exponential function of the reciprocal of a temperature. Therefore, the temperature detection signal is nonlinear with respect to the temperature. As the results in low resolution at a high temperature and at a low temperature, the accuracy of measurement is low.
Meanwhile, a platinum (Pt) resistor having good linear output characteristics can be used instead of the thermistor. However, the use of the platinum resistor, which is expensive, raises the price of the measurement device.
A configuration described in Japanese Unexamined Patent Application Publication No. 2003-75266 is adapted to improve the accuracy of gas temperature detection. More specifically, a linear gas temperature signal is output by connecting a resistor and a thermistor in parallel or by connecting a plurality of resistors in parallel or in series. However, such a configuration of a resistor-based analog circuit exhibits inadequate linearity and provides a narrow output range. Hence, the configuration lowers the level of convenience.
A device described in Japanese Unexamined Patent Application Publication No. 2010-7530 is disposed external to a gas temperature sensor to accurately diagnose a failure of the gas temperature sensor. However, the use of such an external device inevitably results in an increased cost.